Electric annealing-furnace.



No. 861,135. PATBNTBD JULY 2s, 1907. A, L. MARSH.

ELECTRIC AN HEALING FURNACB.

APPLIoA'rIox FILED 2123.18, 1907.

M 721207, VZQWZ QW #QW/Maw UNITED STATES PATENT oEEIeE.

ALBERl L. MARSH, OF LAKE BLUFF, ILLINOIS, ASSIGNOR TO TI'IE IIOSKINS COMPANY, OF CHICAGO, ILLINOIS, A CORPORATION OE ILLINOIS.

ELECTRIC ANNEALING-FURNACE.

Specification of Letters atent.

Patented July 23, 1907.

Application filed February 18, 1907. Serial No. 358.002.

To all whom 'it may concern:

Be it known that I, ALBERT L. MARSH, a citizen of the United States, residing at Lake Bluff, in the county of Lake and State of Illinois, have invented a new and useful Improvement in Electric Annealing-Furnaces, of which the following is a specification.

The object of my invention is to provide a novel construction of portable electric annealing furnace, which shall be adapted, more particularly, for annealing gold in dental work.

n In the accompanying drawing, Figure 1 is a view of my improved furnace in vertical sectional elevation; Fig. 2, a top plan view of; the plate or top of the fur- Anace; and Fig. 3, a plan view of the furnace with the top removed.

- A body 5 of refractory material, as fire-clay, in the preferred circular form illustrated, has an annular chamber 6 formed in its upper side and provided in the surface of its bottom with a spiral groove 7. In this groove is laid, and fastened at intervals, as by tacking, an electrical resistance conductor 8, in the preferred form of a helical wire, made, 'by preference,

n' in accordance with the invention of'United States Patent No. 811,859, granted to me February 6, 1906, because of the high degree of resistance 'it affords in a comparatively short length' of the wire, and of its quality of withstanding high temperature. The helical form of the wire is desirable, as adapting it to resist warping and tendency to fracture under the strains of expansion and contraction to which it is subjected .in use. In the body 5 are shown to be provided; in a plane below the base of the spiral groove, a transverse series of openings 9, to permit the',cireulation` of air through them for keeping the base-portion of the body from becoming excessively hot. The body -is'fastened upon a light-metal stand 10, the legs 11 of which terminate in balls 12 of wood orother suitable'insulating'material. To the under side of the center of the stand is fastened a centrally perforated head 13 of insulating material, as talc, into which the ends of the wire 8 extend covered with insulation and whereinwell-known kind adapted to be inserted into` the socket of an incandescent electric lamp for supplying the-current to heat the resistance conductor 8 and walls of the groove 7. In the chamber 6 fits a capplate or top 15, which is preferably fastened in place, as represented. It is formed of refractory material, such as talc, and constitutes the support for the work undergoing the annealing action ol' the furnace; and it is shown to be provided with an inner shallow circular flange 1G and a similar outer rim ange 17. On flanges 18 projecting horizontally from the upper parts .of the legs 11 is supported and fastened a rest 19 of wood or other suitable heat insulating material, shown in the form of a ring, to surround the body 5 and provide the intervening circumferential air-space 20. The ring affords a rest for the hand of the user of the furnace, in

manipulating with the instrument employed pieces of gold imposed on the plate 15 to be annealed.

With the furnace coupled to a supply of electric current, the wire 8 soon becomes intensely heated, heating the walls of the groove 7 and, by radiation, the top 15, to furnish thereto the requisite annealing heat.

The refractory material` composing the body 5 is a relatively poor conductor of heat, while that composing the top 15 is a relatively good conductor of heat, whereby radiation from the heating-coil tends upwardly against the top, with the advantage of heating it more readily and intensely by avoiding dissipation of the heat through the body.

It will be observed that the conductor 8 is not enibedded in the groove containing it, but is free therein to expand and contract independently of its walls, the coefficient of expansion vof which is less than that of the wire, whereby the walls would soon be fractured by the expansion and contraction of the wire if it were so embedded.

tory material interposed between said top and body, und

an electric resistance conductor confined in said groove and having its ends connected with a conductor for connection with a supply of current.

2. An electric annealing furnace comprising, in combination, :1 body of refractory material formed with a chamber in its upper side, a spiral' groove formed in the base of said chamber, a helical electric resistance wire laid along und confined in said groove und having its ends connected with a conductor for connection with a supply of current,

a top of refractory material covering said chamber, a-

stand on which said body is supported, and a rest of nonheat-conducting material supported on said stand to su'rround suid body.

ALBERT L. MARSH.

In presence of R. A. SCHAEFEn, J. H. LANDES. 

